1. Field of the Invention
The present invention relates to semiconductor device manufacturing equipment. More particularly, the present invention relates to a load-lock and to semiconductor device manufacturing equipment having the same.
2. Description of the Related Art
Typically, a semiconductor device is fabricated by repetitively performing a series of processes, such as photolithography, diffusion, etching, deposition, and metallization processes, on a wafer. The manufacturing equipment for fabricating a semiconductor device includes apparatus for performing each of these processes. Therefore, semiconductor device manufacturing equipment typically includes etching, ion implantation, and deposition apparatus having processing chambers into which a wafer is loaded in a particular sequence. In this respect, the wafer must have a specific orientation relative to the apparatus or else the specific process is not performed with the necessary degree of precision.
Also, particles or contaminants in the air in the respective processing apparatus can adversely affect the production yield. Thus, it is important to keep the interior of the equipment very clean. To this end, each processing chamber of conventional semiconductor device manufacturing equipment is hermetically sealed from the outside and the wafer is processed in a vacuum so that potential contaminants, such as particles, are minimized.
Furthermore, conventional semiconductor device manufacturing equipment also includes a load-lock chamber for accommodating a wafer cassette in which wafers are supported, and a transfer chamber including a robot for transferring wafers from the load-lock chamber to one or more of the process chambers. A vacuum pressure, similar to that prevailing in a process chamber, is created in the load-lock chamber so that the interior of the process chamber does not have to be brought from atmospheric pressure to the vacuum pressure each time a wafer is loaded into the process chamber. This is particularly important in terms of efficiency because the load-lock chamber has a smaller volume than each process chamber and as such, it takes less time to evacuate the load-lock chamber than a process chamber.
Conventional semiconductor device manufacturing equipment as described above may be of a cluster type in which one or two load-lock chambers and a plurality of process chambers are disposed around and connected to the transfer chamber. Furthermore, the semiconductor device manufacturing equipment may include an alignment apparatus for aligning wafers. The chamber of the alignment apparatus is also connected to the transfer chamber. Each wafer removed from the load-lock chamber by an arm of the robot is first introduced into the alignment apparatus so as to be oriented by the alignment apparatus before the wafer is transferred to a process chamber. Accordingly, the load-lock chamber, the transfer chamber, the alignment chamber, and the process chambers are selectively opened and closed during the time a wafer is transferred into and from the chambers. To this end, the semiconductor device manufacturing equipment also includes a respective slit valve interposed between the transfer chamber and each of the load-lock, alignment and process chambers.
As described above, in conventional semiconductor device manufacturing equipment the load-lock chamber is a buffer in which a vacuum is created before the wafer is transferred to a process chamber. Thus, the load-lock chamber provides an environment similar to that within the process chamber, and isolates the environment within the process chamber from the outside air which contains potential contaminants. Furthermore, fumes emanating from the surface of each processed wafer can be diluted and eliminated in the load-lock chamber. Specifically, the wafer is transferred by the robot back into a load-lock chamber after it has been processed in one of the process chambers. Then, a purge gas from an external source is supplied into the load-lock chamber to dilute the fumes. The purge gas is typically nitrogen or argon and is supplied into the load-lock chamber through a purge gas supply line at a rate of several to several tens of sccm. The purge gas supply line is connected to the top of the load-lock chamber. The fumes diluted by the purge gas are removed from the load-lock chamber by a vacuum pump connected to an exhaust port provided at the bottom of the load-lock chamber.
Furthermore, a door is disposed at one side of the load-lock chamber for allowing the wafer cassette to be transferred into and removed from the load-lock chamber. On the other hand, a slit valve disposed on the opposite side of the load-lock chamber serves as a passageway through which the robot arm can enter to extract a wafer from the wafer cassette. In this respect, the wafer cassette supports the wafers so as to lie horizontally when the wafer cassette is supported in the load-lock chamber. An elevator moves the wafer cassette vertically within the load-lock chamber so that each of the wafers supported in the cassette can be extracted by the robot arm. Furthermore, the wafer cassette has an open back that faces the door and through which the wafers can be aligned so that all of the flat zones, for example, of the wafers face in the same direction. The front of the cassette is also open and faces the slit valve in order to allow the robot arm to take the wafers out of the wafer cassette.
However, the conventional semiconductor device manufacturing equipment has the following drawbacks.
First, the supplying of purge gas into the load-lock chamber creates turbulence or an eddy between the back of the wafer cassette and the inner wall of the load-lock chamber adjacent thereto. Any contaminants adhering to the inner wall of the load-lock chamber are dislodged by the turbulence or eddy, thereby generating particles in the load-lock chamber. The particles are blown by the purge gas onto the wafers adjacent the flat zones of the wafers that are exposed at the back of the wafer cassette, thereby contaminating the wafers and reducing the production yield.
Secondly, the slit valve is sometimes opened while the degree of vacuum in the transfer chamber is lower than that in the load-lock chamber. In this case, air is introduced into the load-lock chamber through the slit valve, and dislodges contaminants adhering to the door of the load-lock chamber and/or the inner wall in which the door is formed, i.e., removes contaminants adhering to the side of the load-lock chamber opposite the slit valve. The resulting particles contaminate the wafers near the flat zones of the wafers that are exposed at the back of the wafer cassette, thereby reducing the production yield.